April 25, 2011 -- There's been a decline in the number of deaths among Americans with high blood pressure for heart-related reasons or any cause, but these rates are still higher than in people with normal blood pressure, a study shows.

"Mortality rates are going down for everybody with high blood pressure, but despite the availability of several types of medication to reduce blood pressure, there is still a large gap between those with hypertension [high blood pressure] and those without," says study researcher Earl S. Ford, MD, MPH, medical officer with the U.S. Public Health Service at the CDC, in a news release.

Ford analyzed data from two national health surveys in his research published in the April 25 issue of Circulation. One set of results came from nearly 11,000 people participating in the National Health and Nutrition Examination Survey (NHANES I) between 1971 and 1975. The second set looked at almost 12,500 people enrolled in NHANES III between 1988 and 1994.

Roughly 30% of U.S. adults have high blood pressure (readings of 140/90 or above), which puts them at greater risk for heart attack, stroke, and kidney disease. Hypertension has been called a "silent killer" because it often has no symptoms.

Tracking Death Rates for Those With Hypertension

Ford examined the changes in death rates for adults ages 25 to 74 from these two large trials with follow-up periods of more than a decade.

Some of his key findings:

The overall death rate for NHANES I participants with high blood pressure was 42% higher compared to adults with normal blood pressure.

The death rate fell from 18.8 deaths per 1,000 people with high blood pressure per year among NHANES I participants to 14.3 per 1,000 people with hypertension per year among NHANES III participants.

The death rate among African-Americans with high blood pressure was higher than that among whites in both sets of data.

The decline in deaths among men with high blood pressure was more than four times larger than those seen in women with high blood pressure.

Death Rates in Men vs. Women

Among women with high blood pressure, smaller declines in the death rate were found than those seen in men, even though a higher percentage of women were receiving treatment and, on average, they also had larger reductions in their blood pressure readings.

Women also didn't do as well in other factors that would improve their overall heart risk. "Compared with hypertensive men, women gained more weight, were more likely to be diagnosed with diabetes, and were less likely to quit smoking," says Ford.

This relatively small drop in death rates among women "was unexpected and requires confirmation," writes Ford. He suggests that "an increased focus on reducing mortality among hypertensive women is needed."